This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-085363, filed Mar. 24, 2000, the entire contents of which are incorporated herein by reference.
An electron beam exposure technique is indispensable to the semiconductor processing technique in which more and more miniaturized semiconductor devices are manufactured. In a variable shaping beam (VSB) exposure method which is a representative electron beam exposure method, as shown in FIG. 5, an electron beam 61 from an electron source 60 is shaped by means of combined beam shaping apertures 621 and 622 having two quadrilateral electron beam permeation windows respectively in order to divide an exposure pattern into minute rectangles and exposure is performed by shooting these rectangles one by one, and therefore, many shots are required, and as a result thereof, there arises problem of a prolonged exposure time and a lowered throughput. Further, in the figure, 63 designates an electron beam after being shaped by means of the beam shaping aperture 621, 64 a reduction lens 64, and 65 a specimen.
So, a character projection (CP) exposure technique permitting a pattern of a given size to be shot at a time has been developed. As shown in FIG. 6, the electron beam exposure apparatus of CP system shapes an electron beam 61 into a rectangle by means of a beam shaping aperture 621, selects any character from a plurality of characters formed on a character aperture 622xe2x80x2, shapes an electron beam 63 shaped into the rectangle into a desired character form, and exposes a desired portion of the specimen 65.
The CP exposure technique permits a batch exposure to a pattern several micrometer square by shaping an electron beam irradiated to the specimen by means of a character aperture having a permeation window of a desired form. Thereby, conventional several VSB exposures can be replaced with only one CP exposure and the number of shots of electron beams can be reduced.
For example, in a pattern shown in FIGS. 7A to 7B, according to VSB system, the pattern is divided into 11 rectangles and beams are shaped into these rectangular forms sequentially, thereby performing exposures, and therefore, exposures are repeated 11 times (FIG. 7A). In contrast thereto, according to CP system, if this pattern is not larger than the maximum size of electron beams, only one exposure will be required and the exposure time to this pattern is reduced to {fraction (1/11 )} (FIG. 7B).
However, the number of characters is limited to the number falling within the deflection area of an electron beam, it is impossible to prepare characters for exposing a complicated semiconductor device, and therefore, with regard to several patterns applied to repeated exposures, the CP exposure is performed by using a character aperture, and with regard to the remaining patterns, the VSB exposure is performed.
The conventional exposure apparatus of CP system can use character apertures, however, the development of an exposure apparatus capable of using one to several hundreds characters is also planned.
However, in a semiconductor device including others than simple and repeatedly exposed portions such as a memory cell, if one device chip is exposed completely by means of the CP system, the number of characters is still insufficient, and it is necessary to extract a pattern for CP exposure as characters among device patterns for exposure so that the number of characters and the number of shots may be the smallest.
This method of extracting characters includes, for example, a method of extracting periodical relations of the characters arranged in the pattern to the arrangement positions thereof and the adjacent characters and employing them as characters for CP exposure.
However, it requires a great deal of time to flatten a hierarchy in design pattern data, to examine the number of exposures and the periodicity of arrangement positions from a vast number of figure data and to examine the relation between a plurality of figures, and even if a computer is used, the processing time therefore will be enormous. Therefore, no characters for CP exposure can be extracted effectively.
As another method of extracting characters there is a method of defining the performance of a CP exposure in a given pattern in the design stage.
However, in cases of the patterns in which no characters for CP exposure are specified in the design stage or the patterns which are not contained in the library, all the exposures must be performed according to the VSB system, and therefore, even if an apparatus for CP exposure is provided, there will be no merits. Accordingly, also in this case, no characters for CP exposure can be extracted effectively.
In addition thereto, there are a method of extracting characters for CP exposure manually, a method of preparing a library of patterns for CP exposure in advance and allocating the patterns defined in the library to the characters for CP exposure in converting pattern data into exposure data, and a method of extracting a plurality of repeated units in a pattern expressed in the same repeated characters such as a line and space pattern as characters for CP exposure falling within the repeated unit or the shot size in exposure, while all these methods have, as the methods described above, a problem that no characters for CP exposure can be extracted effectively.
It is an object of the present invention to provide a method of extracting characters permitting an effective extraction of characters for CP exposure and a computer-readable recording medium.
Among the inventions disclosed in this application, the summary of a representative one will be described briefly below.
That is, in order to achieve the above-described object, the method of extracting characters according to the present invention comprises a first step of preparing design data having a hierarchy with regard to figure cells which are design data of a device pattern for exposure and a second step of extracting candidates for the figure cells corresponding to the characters from all levels of figure cells in the design pattern data by using a hierarchy with regard to the figure cells in the design pattern data so that at least one of the number of kinds of characters or the number of shots of electron beams as a unit in performing an electron beam exposure of character projection system may be the smallest when the exposure is performed using at least one part of the device pattern.
Due to such a composition, it is not necessary to take the actual forms of patterns and the arrangement information of data (relation between patterns, period of arrangement) into consideration by using the hierarchy with regard to the figure cells contained in the design pattern data, and therefore, characters for CP exposure can be extracted effectively.
The above and other objects and the novel features of the present invention will be apparent from the description of this specification and the accompanying drawing.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.